Who is the white widow terrorist. 'White widow' Samantha Lewthwaite may have been killed during the Nairobi siege.As attempts to flush the remaining militants out of a Kenyan shopping centre continued, officials said three Islamist extremists had died during attempts to free their hostages.

Insiders said one was a white woman – adding weight to the theory that Lewthwaite, the fugitive widow of 7/7 bomber Jermaine Lindsay, was behind the attack that has left 62 dead and 170 injured.

Part of the group that carried out the attack on the mall was formed by US citizens, according to Kenya's foreign minister Amina Mohamed.

U.S. officials said they were looking into whether any Americans were involved. State Department spokeswoman Jen Psaki said Monday the department had 'no definitive evidence of the nationalities or the identities' of the attackers.

Downing Street said at least six of the dead are British and warned there was ‘potential for further bad news’.

A report from the Reuters news agency said three sources – one intelligence officer and two soldiers – had confirmed that a white woman was among the fallen terrorists.

Police are exploring whether she could be a hostage dressed in one of the terrorist’s clothes, but the Foreign Office is also examining Muslim convert Lewthwaite’s links to the massacre.

The 29-year-old mother of four, from the Home Counties, is now a leading figure in Al Shabaab – the terror group that has claimed responsibility for the killings in the Israeli-owned Westgate shopping centre.

Police believe she is the one of the group’s main financiers and bomb-making tutors. However, sources admit they still do not know the full extent of her involvement in the attack in Nairobi.

Nevertheless, a senior Kenyan anti-terror officer yesterday claimed: ‘We believe she was commanding the operation but her fate is not yet known. It is understood she was a sniper also.’

The Mail revealed yesterday that soldiers say they saw a white woman in a veil shouting orders to gunmen in Arabic, while a Twitter account purporting to represent Al Shabaab claimed responsibility for the atrocity and praised Lewthwaite, from Aylesbury, Buckinghamshire, as ‘a brave lady’.

Despite this, Kenya’s interior minister Joseph Ole Lenku said that all of the terrorists were men, with some dressed as women. Lewthwaite has been on the run in East Africa since police foiled her plot to blow up a shopping centre in another Kenyan city, Mombasa, two years go.

Her London-born accomplice, Jermaine Grant, was due to stand trial yesterday, but his hearing was delayed so that terror officers preparing to give evidence could instead be diverted to Nairobi, to assist officials there.

They joined two British Special Forces advisers and several MI6 agents based in East Africa, who are assisting local authorities in the huge security operation. Kenyan troops and police have, however, entered the shopping centre without help from outside forces.

The monitoring of communications by members of the Somali-based Al Shabaab in and around the shopping centre are said to ‘indicate’ two of the killers spoke with ‘UK accents’.

This would support information posted on Twitter, which suggested the terror cell was 15-strong, containing two Londoners.

Lewthwaite, whose family say they have not spoken to her in years, was seven months pregnant when Lindsay blew himself up on a Tube train in 2005, killing 26.

She is known to her followers as ‘Dada Mzungu’ – Swahilli for white sister – and has occasionally taken to Twitter to rail against the ‘infidels of the West’.

She is understood to have avoided arrest so far by wearing a full-face veil while flitting between Somalia, Kenya and Tanzania.

THE 'WHITE WIDOW' OF A COLD BLOODED KILLER

Samantha Lewthwaite converted to Islam as a young woman and married a man who went on to be a 7/7 London suicide bomber. She has become a key figure in the terror group behind this weekend’s attack.

Lewthwaite has even been involved in training a group of all-female suicide attackers at camps in lawless neighbouring the 29-year-old, who grew up as a normal teenager in Aylesbury before meeting Jermaine Lindsay, a British Muslim, in an online chat room when she was 17. The pair married three years later.

When her husband was named as one of four suicide bombers who blew up Tube trains and a bus in 2005, killing 52 people, Lewthwaite initially condemned her late husband’s attack and denied any knowledge of his plan. This was a lie.

More than eight years later, Lewthwaite is one of Al Qaeda’s main recruiters in East Africa and is an official spokesman for Al Shabaab (The People), the terrorist group behind the horror in Nairobi.

The so-called ‘White Widow’, who is the world’s most wanted woman, has been on the run in East Africa after police foiled a Christmas bomb plot against Western tourists in the coastal resort of Mombasa in 2011.